linguistics as a natural science

Linguistics is often referred to as a social science, often housed academically in anthropology departments since anthropologists must study linguistics as a symbol system of cultural meanings and values, which are obviously among the central concerns of the anthropologist. But there's an aspect of linguistics that is as "hard" a science as physics or biology. That's language structure, as distinct from language use. Its methods are mathematical in the case of syntax, and mathematical logic in the case of semantics. 

So what's this hard vs social difference amount to? In the social sciences, the study has to account for human choices, the choices individuals make for themselves and the choices forced upon them by others. Policy, politics, war, fashion, ideology all impact societies and their economies and individual psychology as well. This makes it hard for the social sciences to predict human behaviors, since there's always a chance that if humans learn about the prediction, they might choose to game the prediction or just buck it out of spite or willfulness. 

But the structure of a language is not a choice. It is a given, learned in childhood. What speakers do with that structure depends on choices, but the structure not. Language has to have a common, shared structure in order to communicate, which is an essential, though not exclusive, purpose of language, and language would likely never have evolved if it didn't have such stability across communicants. And even if it evolved solely as an individual cognitive assist, its communicative function has evolved into the indispensable means for cultural transmission upon which tribal success depends. It's no surprise that the only language of radically limited structure is Pirahã, spoken by a tribe extremely remote from contact and competition from other tribes. The pressure for complex communication is likely low there. One might argue that Pirahã is the exception that proves the rule and explains the emergence of the rule. 

This "hard" aspect of the social science is not unique to linguistics. Economic laws -- supply and demand, Say's and Jevons laws, etc. -- have this hardness, and it doesn't prevent the science from being impossible to predict with certainty. There's a world of choices between cup and lip. Same is true of physics -- it also has limited capacity to predict actual events. It's just that we demand economists to predict, and they foolishly step into that dogshit arena just outside the door of the ivory tower.